Magnetic powder applicator

ABSTRACT

An applicator for uniformly applying magnetically responsive dry particulate material to broad areas on a web moved past the applicator to deposit the material in pattern areas attracting the material thereto. The applicator comprises an applicating roller having a plurality of magnetic members arranged about a shaft within a rotatable non-magnetic sleeve to provide a magnetic field around the roller having a feed zone with a radial field changing to a tangential field, an applicating zone with a stronger radial field following the feed zone and a return zone extending from the applicating zone to the feed zone and having a stronger tangential field immediately following the applicating zone. A scavenging roller has a plurality of magnetic members arranged about a rotatable shaft within a non-magnetic sleeve to carry any free particulate material applied by the applicating roller away from the web surface and back to a tray.

United States Patent [1 1 Kangas et al.

[ MAGNETIC POWDER APPLICATOR [75] Inventors: Larry G. Kangas, St. JosephTwp.,

St. Croix County, Wis.; Robert J. Kline, Grant Twp., Washington County,Minn.

[73] Assignee: Minnesota Mining & Manufacturing Company, Saint Paul,Minn.

[22] Filed: June 4, 1971 [21] Appl. No.: 150,176

Related U.S. Application Data [62] Division of Ser. No. 867,768, Oct.20, 1969.

[52] U.S. Cl. 118/637, 117/17.5 [51] Int. Cl G03g 13/00 [58] Field ofSearch 118/637, 623;

[56] References Cited UNITED STATES PATENTS 3,572,289 3/1971 Maksymiak118/637 3,640,248 2/1972 Nielander 118/637 3,457,900 7/1969 Drexler118/637 2,975,758 3/1961 Bird, .lr. 118/637 3,392,432 7/1968 Naumann l118/637 3,592,675 7/1971 Tung-nan Cheng 1l7/17.5

[ 1 June 19, 1973 3,550,556 12/1970 Chawda ..118/637 3,117,891 l/l964Lehmann..... 118/637 [5 7] ABSTRACT An applicator for uniformly applyingmagnetically responsive dry particulate material to broad areas on a webmoved past the applicator to deposit the material in pattern areasattracting the material thereto. The applicator comprises an applicatingroller having a plurality of magnetic members arranged about a shaftwithin a rotatable non-magnetic sleeve to provide a magnetic fieldaround the roller having a feed zone with a radial field changing to atangential field, an applicating zone with a stronger radial fieldfollowing the feed zone and a return zone extending from the applicatingzone to the feed zone and having a stronger tangential field immediatelyfollowing the applicating zone. A scavenging roller has a plurality ofmagnetic members arranged about a rotatable shaft within a non-magneticsleeve to carry any free particulate material applied by the applicatingroller away from the web surface and back to a tray.

8 Claims, 5 Drawing Figures MAGNETIC POWDER APPLICATOR This applicationis a division of application Ser. No. 867,768, filed Oct. 20, 1969.

This invention relates to an applicator for applying a uniform layer ofmagnetically responsive dry particulate material to particle-attractiveareas on a moving, differentially particle-attractive surface.

The present invention is particularly useful in applying pigmentedparticulate material to an article to de velop an image thereon. Oneexample of such use is in developing imagewise a differentiallyconductive pattern formed by projecting a light image on aphotoconductive web. The photoconductive web being positioned between aninsulative layer, backed by an electrode, and a second electrodecontacting the particulate or powder which is in electrically conductivecontact between the second electrode and the photoconductive web.

The prior art is replete with magnetically responsive powder applicatorsin which permanent magnets are arranged about a shaft within anon-magnetic outer sleeve, and the shaft and the sleeve are mounted forrelative rotation. Recently, as illustrated by US. Pat. No. 3,455,276,it has been found advantageous in such devices to utilize magneticmembers formed of fine grain permanent magnet material dispersed in anonmagnetic immobilizing matrix. With such magnetic members it ispossible to present an even deposition of particulate material ordeveloper powder to an imagebearing member with a width of eight andone-half inches to thirteen inches since the magnetic field along themagnetic members can be made constant for such length unlike otherpermanent magnets. While such an applicator does present a uniform layerof particulate material to a photoconductive web the desired uniformlayer of particulate material on the particle attractive areas of theweb has not been achieved. As the particulate material is transferredfrom the sleeve of the applicating roller to the photoconductive webwhere the attractive force on the web overcomes the magnetic attractionof the applicating roll, the powder extends between the web and thesleeve. As the web is advanced, the particulate material separates fromthe sleeve and forms tree-like piles on the web with the particles inthe uppermost portion of the piles weakly attracted or free on the web.As the web continues to move along, these free particles may then becomedislodged and come to rest on the non-attractive (e.g., background)areas of the web. Furthermore, upon transferring the particulatematerial from the photoconductive web to a sheet of copy paper to forman image thereon the nonattracted particles may be dispersed onto areasof the copy paper where they are not desired. In either case thesedislodged particles will darken or change the image resolution on asheet of copy paper which is highly undesirable.

According to the present invention, an improved applicating rollerutilizing magnetic members formed of fine grain permanent magnetmaterial dispersed in an immobilizing matrix is provided. The presentinvention also provides an apparatus for applying a uniform layer ofmagnetically responsive particulate material to particle-attractiveareas on a moving differentially particleattractive web such that theparticles applied to the web are all attracted thereto. The presentinvention further provides an applicator for presenting a dimensionallyuniform coating of magnetically responsive particulate material to awide, differentially particleattractive surface to deposit theparticulate material in the particle-attractive areas.

The apparatus illustrated is adapted for applying a layer ofmagnetically responsive .dry particulate material to particle attractiveareas on a moving differentially particle attractive surface andcomprises an applicating roller and a scavenging roller, each rollercomprising a magnetically permeable shaft, a plurality of generallysector-shaped strips of magnetic material, said strips being magnetizedto create axially extending areas of alternating polarity in adjacentcircumferential position about said shaft, and a non-magnetic sleevefitted over the magnetic strips, means for mounting the sleeve and theshaft of the applicating roller for relative rotation to carryparticulate material on the sleeve to a said moving surface, and meansfor mounting the sleeve and the shaft of the scavenging roller to carryany non-attracted or free particulate material around the sleeve awayfrom a said surface.

The novel features and advantages of the present invention will becomeapparent after reading the following description which refers to theaccompanying drawing wherein:

FIG. 1 is a longitudinal elevational'view of a particulate materialapplicator made in accordance with the present invention;

FIG. 2 is an end elevational view of the applicator of FIG. 1;

FIG. 3 is a diagrammatic vertical sectional view of the operation of theapplicator of FIG. 1;

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 1; and

FIG. 5 is a perspective view illustrating one magnetic member.

A magnetically responsive dry particulate material applicator made inaccordance with the present invention and generally designated 10, isillustrated-in FIG. 1 and comprises an applicating roller 12 and ascavenging roller 14 supported with their peripheral surfaces adjacent amoving surface 16 having areas differentially attractive to theparticulate material. In the illustrated embodiment, the rollers 12 and14 are supported by frame members 17 comprising a pair of end plates 18and 19, a developer powder tray 21 extending between the rollers 12 and14, and a developer powder hopper 23 extending between the end plates 18and 19 above the powder tray 21.

The applicating roller 12 comprises a shaft 25 formed of a materialhaving a high magnetic permeability, such as soft iron, stationarilysupported at opposite ends in the frame members 1.7. Positioned abovethe shaft 25 are four generally sector-shaped strips of magneticmaterial 27, which will be described in greater detail hereinafter.Rotatably mounted relative to the shaft 25 coaxially therewith, as bybearing mounted end caps 32 is a non-magnetic cylindrical sleeve 33formed of a material (e.g., glass, aluminum, or polymeric material)which will not shield the magnetic field from the magnetic strips 27. Atone end the sleeve 33 is formed with a pulley 34 about which a drivebelt 36 passes to rotate the sleeve 33 about the magnetic strips 27. Thedrive belt 36 also passes around an idler roller 38, a bail shaft pulley39 and a drive pulley 40. The drive pulley 40 is suitably driven from adrive motor 42 through gears in a gear box 41.

As desired in some copyingapplications, the applicating roller 12 servesas an electrode; therefore, it is desired to connect the sleeve 33 to asource of electrical potential; and in the illustrated embodiment aconnector 43 is attached to the shaft 25, to which a lead from a sourceof a potential may be coupled. The sleeve 33 is electrically connectedto the shaft 25 by sliding leaf 44 (FIG. of resilient conductivematerial. The sleeve 33 in this example is preferably formed ofaluminum, but could be formed of another nonmagnetic material such asglass with an electrically conductive, non-magnetic surface coating.

The applicating roller 12 is positioned adjacent the tray 21 in parallelaligned spaced relation to the moving differentially particle-attractivesurface 16, defined by the surface of a web comprising, for example adifferentially light struck photoconductive coating 46 carried on aninsulative backing 48 supported in turn on an electrically conductivesurface 47. In any instance, if the moving surface of the web 16 is tobe coated, it carries an undeveloped differential image pattern to whichis to be applied an even coating of particuate image-formingmagnetically responsive material hereinafter referred to as developerpowder 49, which may be supplied by the applicating roller 12 from asupply disposed in the tray 21.

Along the edge adjacent the applicating roller 12, the tray 21 is formedwith an inclined surface defining a doctor blade 51 spaced from thesleeve 33 of the applicating roller 12 to define a doctor gap with thesleeve 33 across the width of the moving surface 16 through which thedeveloper powder 49 must pass to be applied to the moving surface 16.

Like the applicator roller 12, the scavenging roller 14 comprises ashaft 54 formed of a material having a high magnetic permeability, suchas soft iron, supported at opposite ends in the frame members 17.Positioned about the shaft 54 are similar generally sector-shaped stripsof magnetic material 55, which will be described in greater detailhereinafter. Anon-magnetic cylindrical sleeve 57 formed of a materialwhich will not shield the magnetic field from the magnetic strips 55 issupported coaxially with the shaft 54. Like the applicating roller 12the sleeve 57 and the shaft 54 of the scavenging roller 14 arerelatively rotatable, however, unlike the applicating roller 12 thesleeve 57 of the scavenging roller 14 is fixed while the shaft 54 isrotatable. The sleeve 57 of the scavenging roller 14 has an insulatingextension 58 secured along its length to mate with the edge of the tray21 opposite the doctor blade 51. This forms a continuous surface alongthe base of the tray 21 around the scavenging roller sleeve 57 and intothe tray 21. The scavenging roller shaft 54 is suitably bearinged in endcaps 57 (only one of which is shown) of the sleeve 57. At one end theshaft 54 extends through an end cap 59 and supports a roller 61 which issuitably driven, such as by a roller 63 that contacts an extension ofthe moving surface 16 and the roller 61, to provide rotation of theshaft 54 and the magnetic strips 55 in a counterclockwise direction asviewed in FIG. 3.

The magnetic strips 27 and 55 are generally shaped as sectors of ahollow cylinder having radially inner faces concavely curved and convexradially outer surfaces joined by radially extending edge walls. In eachroller 12 or 14 the magnetic strips 27 or 55 are arranged in a circulararray about their associated shaft 25 or 54 with their edges generallyradial and in sideby-side relation. The strips 27 and 55 are formed byextrusion of a non-magnetic matrix which may be a resinous or plasticcomposition, and an elastomeric semisolid, or viscous liquid, capable ofhardening, setting or being cured to a solid state in which is evenlydispersed anisotropic ferrite domain-sized particles, which particlesare capable of achieving physical orientation when acted upon byinternal shear stresses. Examples of the particles are certainfine-grained, permanent magnet materials, particularly the ferrites ofbarium, lead, and strontium which are easily magnetized to saturation.The matrix may be natural rubber with compound agents, plasticizers,vulcanizing agents, and the like to provide the hardness of the matrixdesired, or may be a thermoplastic or thermosetting material, as forexample, polyvinyl chloride. Preferably the ferrite particles areoriented such that each particle (as illustrated diagrammatically inFIG. 5 at 63) is positioned with its magnetic poles positioned radiallyrelative to each other.

In the applicating roller 12, since the shaft 25 is fixed, the magneticstrips 27 are constantly positioned as schematically illustrated in FIG.3. The strips 27 are arranged about the shaft 25 with the edges thereofgenerally radial and in side-by-side relation to substantially form acylinder and they are magnetized to provide peripheral circumferentialareas of constant polarity extending the lengths of the strips withadjacent areas oppositely polarized. Two such peripheral areas providedby a single magnetic strip 31 are illustrated in FIG. 5. The magneticstrips 27 produce the relative magnetic field component strengthsillustrated in FIG. 4 where the radial field component is illustrated indotted lines and the tangential field component is illustrated in fulllines. The magnetic field just prior to and at the doctor blade 51 isgenerally exclusively radial thereby tending to align the developerpowder particles in rows standing out perpendicularly from the surfaceof the sleeve 33. As the sleeve 33 rotates the doctor blade may thentrim these rows of particles to pass particles through the doctor gap. Astronger tangential field is developed immediately past the doctor blade51 to draw the powder passing the doctor gap against the sleeve 33 toimprove the powder flow toward the moving surface 16. The radial fieldat the doctor blade together with the tangential field immediatelythereafter define a powder feed zone.

Along the line nearest the moving surface 16 and to both sides thereofis an applicating zone. In the applicating zone the magnetic field isnearly exclusively radially oriented, thereby tending to align thedeveloper powder particles in rows extending outward radially from thesleeve 33 to increase the density of powder contacting the movingsurface 16. A uniform layer of developer powder is thereby presented tothe photo conductive surface 46. The web 46 may then selectively attractdeveloper powder from the applicator sleeve 33 according to the imagepattern thereon while maintaining a space between the sleeve 33 and theweb 46 to prevent powder from being pressed onto nonattractive areas ofthe web.

Moving about the sleeve 33 counterclockwise (as viewed in FIG. 3 or 4)away from the moving surface 16 is a powder return zone in which themagnetic field is rapidly changed to a dominant tangential fieldstronger than that in the feed zone to lay the rows of developer powderparticles against the sleeve 33 to aid in moving any n0n-attractedparticles away from the moving surface. Continuing in a counterclockwisedirection about the applicating roller 12 the return zone extends to thefeed zone and the magnetic field has a sufficient strength to carry theremaining non-attracted developer powder on the sleeve 33 back into thetray 21..

The unique magnetic field about the applicating roller 12 isaccomplished by the size, polarization and positioning of the fourmagnetic strips 28, 29, 30 and 31. The weak radial field of the feedzone at the doctor blade 51 is generally provided by a four poleapproximately 35 sector magnet 28. The weak tangential field of the feedzone is provided by the 35 four pole magnet 28 and a first two pole 90sector magnet 29 abutting the 35 four pole magnet 28. Due to its massthe first two pole 90 sector magnet 29 also generally provides thestrong radial field in the applicating zone and cooperates with a secondtwo pole 90 magnet 30, that is adjacent and spaced from it, to providethe strong tangential field of the return zone. A four pole 90 sectormagnet 31 abuts the second 90 two pole magnet 30 and is adjacent andspaced from the 35 four pole magnet 28 to complete the array of magnets.The magnet 31 provides a sharply varying magnetic field near the end ofthe return zone to promote increased tumbling action as the returnedpowder mixes in the tray with the supply powder.

As in the applicating roller 12, the magnetic strips 55 of thescavenging roller 14 are arranged about the shaft 54 with the edgesthereof generally radial and side-byside relation to form a cylinder andthey are magnetized to provide peripheral circumferential areas ofconstant polarity extending the length of the strips 55 with adjacentareas oppositely polarized. However, unlike the applicating roller 12,the magnetic strips 55 are all similar, 90 sectors each of which ismagnetized to provide a north pole and a south pole, generally of equalstrength, on its peripheral surface. These strips 55 have sufficientmagnetic strength to pull any free powder particles on thephotoconductive web 46 against the sleeve 57.

A bail shaft 67 is rotatably supported above the developer powder tray21 and extends parallel to the rollers 12 and 14. The bail shaft 67 isbearinged in the frame members 17 and extends through one end thereof tocarry the bail pulley 39 so as to be suitably driven by the motor 42.Two h'elical springs 68 extend perpendicularly from the bail shaft 67,one generally at each end of the tray 21, and a wire bail 69 issupported at the free ends of the springs 68 to normally lie parallel tothe bail shaft 67.

In use, a differentially exposed photoconductive web 46 is moved firstpast the applicating roller 12. As it does so, the developer powder 49is moved from the tray 21 through the doctor gap and into contact withthe web 46 on the applicating roller sleeve 33. Developer powder istransferred to the particle-attractive areas on the web 46 correspondingto the images carried thereon. As the developer powder on the sleeve 33separates from the powder applied to the web 46 tr'eelike piles ofdeveloper powder are formed at the imaged areas on the web. Any powdercarried into contact with non-attractive areas of the web continues tobe carried on the sleeve 33 around the applicating roller 23 and backinto the tray 21.

As the web 46 continues to be moved, it passes under the scavengingroller 14. As the tree-like piles of developer powder on the image areasof the web 46 pass under the scavenging roller 14 any weakly attractedpowder at the tops of the trees or free powder on nonv attractive areasof the web is attracted to the sleeve 57 of the scavenging roller 14 bythe magnetica strips 55. While the shaft 54, and therefore, the magneticstrips 55 arerotated counterclockwise, as illustrated in FIG. 1, thepowder attracted to the surface of the sleeve 57 progresses in atumbling fashion around the sleeve in a clockwise direction (oppositethe direction of rotation of the magnets) and thereby into the tray 21.Any powder returned to the tray by the scavenging roller 14 againbecomes available as supply for the applicating roller 12, powdersupplied adjacent the scavenging roller 14 being moved toward theapplicating roller 12 by rotation of the bail shaft 67 and the bail 69.

In one specific operative embodiment the applicating roller sleeve 33 isaluminum with a wall thickness of 0.025 inch and an inside diameter toprovide an air gap of about 0.012 inch between its inner surface and theperiphery of the magnets 27. The sleeve 33 is spaced from thephoto-conductive web 46 0.013 inch with a tolerance of plus or minus0.002 inch. The gap at the doctor blade 51 is made 0.010 inch with atolerance of plus or minus 0.002 inch and the center of the doctor bladeis spaced about 60 (clockwise as viewed in FIGS. 3 and 4) from avertical plane intersecting the axis of the applicating roller 12.

The strength of the radial field component in the applicating zone whenmeasured on the outside of the aluminum sleeve 33 is about 400 gaussprovided primarily by the first two pole sector magnet 29. This radialfield strength will produce an applicating zone on the planarphotoconductive web 46 which extends across the web 46 and which isbetween-0.75 inch and 1.0 inch wide when the sleeve 33 is rotated atone-tenth the web speed in a direction opposite to the movement of theweb 46.

The sleeve 57 of the scavenging roller 14 is preferably spaced from theweb surface about 0.l25 inch to 0.150 inch. The scavenging rollermagnets 55 are rotated by rotation of their shaft 54 at a speed betweenrpm and 500 rpm, preferably about 300 rpm.

We claim:

1. Apparatus for applying a uniform layer of magnetically responsive dryparticulate material to particleattractive areas on a movingdifferentially particleattractive surface, comprising:

a pair of spaced rollers supported with their peripheral surfacesadjacent a said moving surface, each. said roller comprising:

a shaft of high magnetic permeability material,

a plurality of elongated generally sector-shaped in cross-section stripsof magnetic material formed of fine grain permanent magnetic materialdispersed in a non-magnetic immobilizing matrix, said strips beingarranged in a circular array about said shaft with the edges of saidstrips generally radial and in side-by-side relation to form at least apartial cylinder, each said strip being radially polarized with constantpolarity along its length and adjacent strips being oppositely polarizedalong their adjacent edges, and

a non-magnetic hollow cylindrical sleeve mounted coaxially with saidarray of magnetic strips and said shaft,

means for mounting said sleeve and said shaft of the first of saidrollers for relative rotation to carry a quantity of said particulatematerial on the periphery of said first roller sleeve to a said movingsurface, and

means for mounting said sleeve and said shaft of the second of saidrollers for relative rotation to carry free particulate material on theperiphery of said second roller sleeve away from a said surface.

2. Apparatus as recited in claim 1 wherein each of said strips ofmagnetic material has an axial length of between 8 and inches.

3. Apparatus as recited in claim 1 wherein said sleeve of said firstroller is electrically conductive.

4. Apparatus as recited in claim 7 wherein said shaft of said firstroller is fixed and said sleeve is supported for rotation about saidshaft and wherein said sleeve of said second roller is fixed and saidshaft is supported for rotation within said sleeve.

5. Apparatus as recited in claim 4 including means for rotating saidsleeve of said first roller and said shaft of said second roller in thesame direction having tangential components at their peripheral portionsnearest the differentially particle-attractive surface that are oppositeto the direction of movement of the surface past the periphery of saidsleeves of said rollers.

6. Apparatus as recited in claim 5 including a tray extending betweensaid first and second rollers for storing a supply of said magneticallyresponsive dry particulate material in which said first roller sleevemay come in contact and for receiving said particulate material removedfrom said moving surface by said second roller and including means fortransferring particulate material collected adjacent said second rollerto a dispensing position adjacent said first roller.

7. Apparatus as recited in claim 6 wherein said shaft of said firstroller is fixed and said sleeve is supported for rotation about saidshaft and wherein said sleeve of said second roller is fixed and saidshaft is supported for rotation within said sleeve.

8. Apparatus as recited in claim 7 wherein each of said strips ofmagnetic material have an axial length of between 8 and 15 inches.

1. Apparatus for applying a uniform layer of magnetically responsive dryparticulate material to particle-attractive areas on a movingdifferentially particle-attractive surface, comprising: a pair of spacedrollers supported with their peripheral surfaces adjacent a said movingsurface, each said roller comprising: a shaft of high magneticpermeability material, a plurality of elongated generally sector-shapedin crosssection strips of magnetic material formed of fine grainpermanent magnetic material dispersed in a non-magnetic immobilizingmatrix, said strips being arranged in a circular array about said shaftwith the edges of said strips generally radial and in side-by-siderelation to form at least a partial cylinder, each said strip beingradially polarized with constant polarity along its length and adjacentstrips being oppositely polarized along their adjacent edges, and anon-magnetic hollow cylindrical sleeve mounted coaxially with said arrayof magnetic strips and said shaft, means for mounting said sleeve andsaid shaft of the first of said rollers for relative rotation to carry aquantity of said particulate material on the periphery of said firstroller sleeve to a said moving surface, and means for mounting saidsleeve and said shaft of the second of said rollers for relativerotation to carry free particulate material on the periphery of saidsecond roller sleeve away from a said surface.
 2. Apparatus as recitedin claim 1 wherein each of said strips of magnetic material has an axiallength of between 8 and 15 inches.
 3. Apparatus as recited in claim 1wherein said sleeve of said first roller is electrically conductive. 4.Apparatus as recited in claim 7 wherein said shaft of said first rolleris fixed and said sleeve is supported for rotation about said shaft andwherein said sleeve of said second roller is fixed and said shaft issupported for rotation within said sleeve.
 5. Apparatus as recited inclaim 4 including means for rotating said sleeve of said first rollerand said shaft of said second roller in the same direction havingtangential components at their peripheral portions nearest thedifferentially particle-attractive surface that are opposite to thedirection of movement of the surface past the periphery of said sleevesof said rollers.
 6. Apparatus as recited in claim 5 including a traYextending between said first and second rollers for storing a supply ofsaid magnetically responsive dry particulate material in which saidfirst roller sleeve may come in contact and for receiving saidparticulate material removed from said moving surface by said secondroller and including means for transferring particulate materialcollected adjacent said second roller to a dispensing position adjacentsaid first roller.
 7. Apparatus as recited in claim 6 wherein said shaftof said first roller is fixed and said sleeve is supported for rotationabout said shaft and wherein said sleeve of said second roller is fixedand said shaft is supported for rotation within said sleeve. 8.Apparatus as recited in claim 7 wherein each of said strips of magneticmaterial have an axial length of between 8 and 15 inches.